1. Field of the Invention
The invention relates generally to telephone line selectors and more particular to telephone line selectors wherein a plurality of telephone lines are controlled by a microprocessor independently of a PBX.
2. Description of the Prior Art
Presently, in situations where a large number of telephone units are used by an organization it has been found that it is economical to use a PBX (Private Branch Exchange) as an interface between telephone lines provided by commercial telephone company and the organization's internal telephone network. The PBX permits a large number of internal telephone units to effectively use a small number of outside telephone lines. Outgoing calls go through the PBX and are directed to available outside telephone lines. Incoming calls are directed to the appropriate telephone unit through the PBX. Internal calls are made through PBX which connects one internal line to another.
With a PBX alone it is not possible to break up an organization's internal telephone system into groups of phones which are associated by work groups within the organization such that a call coming into that work group could be answered by a secretary assigned to that particular work group.
This shortcoming has been partially overcome by the use of a 1A2 key systems in conjunction with a PBX. By connecting a 1A2 key system to a PBX and wiring the telephone units of a work group to the 1A2 key system, it is possible to have a secretary monitor calls for members of the work group. However, the cabling and installation costs of such a system are high. Usually a twenty-five pair wire cable or larger is used in conjunction with the 1A2 key system. The cable is bulky and difficult to run. The wiring must run from the PBX to the place where the work group telephone units are located. The sheer size of the cable and the lengths of the cable needed increase its costs significantly. Also the difficulty in running such a bulky cable through walls or other passages increases the time necessary for installation which means an increase in the installation costs.
When it becomes necessary to move equipment associated with a work group using a 1A2 key system in conjunction with a PBX, the same difficulties and increased expenses are experienced because the entire twenty-five pair cable must be rerouted to the new location.
Furthermore, the 1A2 key system is not controlled by a microprocessor and therefore does not have the flexibility inherent with a programmable system.